Poly(hydroxyalkanoic acid) (PHA) polymers such as poly(lactic acid) (PLA) can be polymerized from renewable sources rather than petroleum and are compostable. They have a broad range of industrial and biomedical applications as films. For example, JP patent application H9-316310 discloses a poly(lactic acid) resin composition comprising PLA and modified olefin compounds. Examples of those modified olefin compounds are ethylene-glycidyl methacrylate copolymers grafted with polystyrene, poly(dimethyl methacrylate), etc., and copolymers of ethylene and alpha-olefins grafted with maleic anhydride and maleimide. Toughened PHA compositions are also disclosed in, for example, US patent application 2005/0131120; U.S. Pat. Nos. 5,883,199, 6,960,374, 6,756,331, 6,713,175, 6,323,308, and 7,078,368; and EP0980894 A1 (films are not transparent).
However, PHAs form brittle cast films of low elongation. Orientation with strain assisted crystallization of amorphous cast film is often used to increase the stiffness or modulus of films as well as elongation. A modulus in the direction of film travel higher than 300,000 psi allows thin film not to elongate highly under tensions that can occasionally happen with continuous film conversion processes. This lower elongation helps to avoid cracking of brittle surface coatings such as glass-barrier coatings or avoids missing registration for printing, performance, or other operations necessary for converting the film into useful finished products. Such orientation processes decrease the elongation-at-break in the direction of the lower orientation. Many continuous film processes require the film being handled to have an elongation at break of more than 2%, so that the film may not break or split during start-up of the line or when the distance between tension control and the tensioning roll is high. Accordingly, it is desirable to obtain a toughener for PHAs that allows a PHA composition to be easily processed as an oriented film into a variety of articles with an acceptable level of toughness, such as improved elongation at break, while retaining the desired high modulus and clarity.